MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY FOR WATER RESOURCES Ph.D Candidate TO VIET THANG STUDY ON ALLOCATION OF WATER RESOURCES AND RATIONAL OPERATION OF RESERVOIRS SYSTEM IN VU GIA – THU BON RIVER BASIN IN DRY SEASON Specialization: Water resoures engineering Code: 58 02 12 Executive summary of Ph.D Thesis Hanoi 2019 This Thesis was completed at: Vietnam Academy for Water Resources Supervisor 1: Assoc Prof, Dr Ngo Le Long Supervisor 2: Assoc Prof, Dr Nguyen Tung Phong Reviewer 01: Reviewer 02: Reviewer 03: The thesis will be defended at the Academic Council of Vietnam Academy for Water Ressources At…… 2019 The thesis can be reached at: - National Library - Vietnam Academy for Water Resources Library MỤC LỤC LIST OF PUBLICATIONS INTRODUCTION Rationale of the thesis Objective the thesis Subject and scope of the research Methodology New contribution of the thesis Structure of the thesis CHAPTER 1: OVERVIEW OF RESEARCH SITUATION AND CALCULATION METHODS OF RESERVOIR OPERATION FOR WATER RESOURCES IN RIVER BASIN 1.1 Overview of research on distribution of river basin water resources in the world and in Vietnam 1.1.1 Literature review of reservoir water allocation using simulation method 1.1.2 Literature review of reservoir water allocation using optimization methods 1.1.3 Literarute review of reservoir water allocation using simulation-optimization method 10 1.2 Literature review of reservoirs in Vu Gia - Thu Bon river basin 11 1.3 Summary of the Rule of inter-reservoir operation (Rule 1537) on the VGTB river basin 12 1.4 Limitations and gaps in the study of inter-reservoir operation and allocation of water resources reasonably at Vu Gia LVS Thu Bon 12 1.5 Conclusion Chapter 1: Approach and orientation of the research steps of the thesis 13 CHAPTER 2: RESEARCH ON SCIENTIFIC BASIS for MODELS OF SUPPLYING WATER RESOURCES AND OPERATING THE SYSTEM OF RESERVOIRING FOR VU GIA THU BON RIVER BASIN - IN THE DRY SEASON 15 2.1 Introduction of reservoir system in Vu Gia - Thu Bon river basin and select reservoirs for research 15 2.2 Building a random simulation model of the flow to the reservoir taken into account the hydrological correlation in the system 16 2.2.1 Determine the type of probability distribution for the flow chain to 04 reservoirs 16 2.2.2 Set up hydrological correlation amongst river branches 16 2.2.3 Tạo chuỗi số ngẫu nhiên thời đoạn 10 ngày tới 04 hồ 17 2.3 Develop a model of operating multi-purpose reservoir system 18 2.3.1 Problem establishment 18 2.3.2 Develop optimal search model and connect to reservoir operation simulation model 20 2.4 Develop a simulation operation model for linkage-reservoir HEC-RESSIM 21 2.5 Conclusion of chapter 22 CHAPter 3: CALCULATION RESULTS OF SYSTEM OPERATION IN VU GIA THU BON RIVER BASIN – to IMPROVE EFFICIENCY OF WATER allocation 23 3.1 Identify scenarios to operate 04 reservoirs 23 3.2 Summary of calculation results of all scenarios 25 3.3 Using HEC-RESSIM model to details calculate selected scenarioes 27 3.3.1 Simulation of operation in 2015 and 2016 27 3.3.2 Simulated operation in 1981-2008 29 CONCLUSIONS AND RECOMMENDATIONS 30 LIST OF PUBLICATIONS Tô Việt Thắng, Ngô Lê Long, Nguyễn Tùng Phong (2018), Research on contribution ratio of large upstream reservoirs for minimum flow in Vu Gia – Thu Bon river system, Hội thảo quốc tế: Water Security and Climate Change (Nairobi, Kenya 12/2018); Tô Việt Thắng (2018), Nghiên cứu tính tốn vận hành hệ thống liên hồ chứa lưu vực sông Vu Gia – Thu Bồn mùa cạn mơ hình HEC-RESSIM, Tạp chí Khoa học kỹ thuật thủy lợi Môi trường 09/2018; Tô Việt Thắng (2018), Method for optimal water allocation of reservoirs system – a casestudy of Vu Gia – Thu Bon River basin, Vietnam, Hội thảo quốc tế: IWA World Water Congress & Exhibition, (Tokyo, Nhật Bản 9/2018); Tô Việt Thắng, Ngô Lê Long, Nguyễn Tùng Phong, Lars Ribbe (2017), Nghiên cứu tạo chuỗi số liệu dòng chảy với mơ Monte Carlo phục vụ tốn phân bổ hợp lý nguồn nước lưu vực sông Vu Gia – Thu Bồn, Tạp chí khoa học cơng nghệ Thủy lợi 02/2017; Tô Việt Thắng, Ngô Lê Long, Nguyễn Tùng Phong (2017), Nghiên cứu xây dựng mơ hình tối ưu phát điện, cấp nước hồ chứa lưu vực sông Vu Gia – Thu Bồn mùa cạn, Tuyển tập hội nghị khoa học Thủy lợi toàn quốc 2017 (có trình bày trước hội nghị); Tơ Việt Thắng, Ngô Lê Long, Nguyễn Tùng Phong (2017), Nghiên cứu mơ chuỗi dịng chảy ngẫu nhiên đến hồ chứa đảm bảo tính đồng thủy văn hệ thống sơng Vu Gia – Thu Bồn, Tuyển tập hội nghị khoa học thường niên 2017 – Đại học Thủy lợi (có trình bày trước hội nghị); Tơ Việt Thắng, Ngơ Lê Long Nguyễn Tùng Phong (2016), Nghiên cứu thiết lập toán phân bổ nguồn nước hợp lý hệ thống hồ chứa đáp ứng nhu cầu sử dụng nước lưu vực sông Vu Gia – Thu Bồn mùa cạn, Tuyển tập hội nghị khoa học thường niên 11/2016 – Đại học Thủy lợi (có trình bày trước hội nghị) 2INTRODUCTION Rationale of the thesis Nowaday, the allocation of water resources among households using water is not a simple problem in many river basins (Harou, Paredes, Solera, & Andreu, 2012) When water demand is low compared to the supply capacity of the system, all water users can coexist without conflict or dispute However, as water demand increases among water users such as households, agriculture, industry, hydropower, etc., conflicts of interest will increase, especially in the dry season (Liu, Chen, & Lou, 2009), leading to difficulties in managing water resource allocation effectively The Vu Gia-Thu Bon river system (VGTB) is the largest interprovincial river system in the central coast of Vietnam The construction of a system of hydroelectric reservoirs on the river has made the management and allocation of water resources to different water users in the river basin become complicated and difficult Conflicts between water use goals become more profound, especially in the dry season requiring a solution of "compromise" between objectives to improve the efficiency of water resource allocation for river basins Therefore, the PhD student has chosen the topic of "Research on allocation of water resources and proper operation of reservoir system in Vu Gia - Thu Bon river basin in dry season" as a doctoral thesis research topic The research content of the thesis will focus on solving the problem of combining simulation and optimization of reservoir system operation, especially in the dry season as a basis to serve the allocation of water from hydropower reservoirs The thesis will focus on researching the scientific basis, setting up the problem, the approach from which to propose simulation-optimal model of inter- reservoir regulation for multi-purpose uses The study will be applied to large reservoirs on the VGTB river system Objective the thesis - Establishing a scientific basis for rational water allocation of reservoir system to meet the needs of VGTB river basin in dry season; - Propose a plan to coordinate the operation of the reservoir system, ensuring intergrated economic efficiency (highest) Subject and scope of the research - Subject of research: Reasonable allocation of water sources for reservoirs A Vuong, Song Bung 4, Dak Mi and Song Tranh on VGTB river basin - Scope of the research: VGTB river basin system in dry season Methodology - The thesis uses the following methods: (i) Method of field investigation; (ii) Methods of statistical analysis; (iii) System analysis method using simulation model and optimization of use in inter-reservoirs operation; (iv) Expert method and community participation; (v) Method of hydrological and hydraulic modeling New contribution of the thesis - Building a scientific basis for operating the reservoir system in rational allocation of VGTB river basin water resources in the dry season; - Proposing the optimal operation rule of the four largest reservoirs in the VGTB river basin, including (A Vuong, Song Bung 4, Dak Mi and Song Tranh reservoirs) to ensure maximum electricity production volume from power generation and harmonization target reservoirs to meet downstream water supply requirements; Structure of the thesis The thesis consists of 130 pages, 17 tables, 54 figures and 55 references In addition to the introduction and conclusion, the thesis consists of chapters: Chapter 1: Overview of related research and methods for reservoir operation and allocation of river basin water sources Chapter 2: Research on scientific basis to build a model of water allocation and rational operation of VGTB river basin reservoir system in dry season Chapter 3: Results of calculation and operation of reservoir system in VGTB river basin to improve the efficiency of water resources allocation 3CHAPTER 1: OVERVIEW OF RELATED RESEARCH AND METHODS OF RESERVOIR OPERATION FOR WATER RESOURCES IN RIVER BASIN 1.1 Overview of research on distribution of river basin water resources in the world and in Vietnam The methods of operation, management and allocation of reservoir in the river basin according to the system operation model can be mentioned as the method of using simulation models, optimization methods and tissue combination methods simulation and optimization (Louck and Eelco van Beek, 2005), (Liu et al., 2009), (Husain, 2012), (Fayaed, El-Shafie, & Jaafar, 2013) and (Ahmad, ElShafie, Razali, & Mohamad, 2014) 1.1.1 Literature review of reservoir water allocation using simulation method In the field of integrated water resources management, the first simulation method was used by the US Army Engineers Association (USACE) to plan and manage Missouri River water resources in 1962 (Rani & Moreira, 2010) Subsequently, the Harvard Water Program applies a technique to simulate the economic designs that apply to water resources (Rani & Moreira, 2010), (Mckinney, Cai, Rosegrant, Ringler, & Scott, 1999) Gradually, complete simulation models were developed and introduced as HEC family models (HEC3, HEC5, HEC RESIM) developed at the Hydrologic Engineering Center (HEC) of US military, serving for reservoir simulation (Rani & Moreira, 2010), (Fayaed et al., 2013) Some other basin simulation models are MITSIM, WUS, MIKEBASIN WEAP These are models that can be capable of simulating complex river basin systems However, although widely used in field of integrated water resources management in general and in simulation of water allocation from reservoir systems in river basins in particular, the simulation method still has a limited point when only provide the best operation plan in simulation scenarios Therefore, in parallel with the simulation method, the optimisation method has been developed and applied in many studies 1.1.2 Literature review of reservoir water allocation using optimization methods Optimization is a method of finding the best option in possible alternatives The most important component in optimization is the objective functions, through which to determine the optimal solutions - the target solution satisfies all the assumptions and constraints John W Labadie (2004) summarized the optimal techniques used in the problem of water allocation from reservoirs and multi-purpose reservoir systems on the same river basin, including a group of implicit stochatic optimization methods and explicit stochatic methods In the past two decades, heuristic algorithms (self-experimental algorithms) have been developed to solve the optimal problem of water allocation, especially the optimal reservoir operation The important benefit of this approach compared to traditional methods is: it can approach the global optimization for a practical problem rather than global optimization for the simplified problem (Maier, 2014) Some newly developed algorithms include genetic algorithms (GA), fuzzy set theory algorithms (FUZZY SET THEORY), Neural network algorithm (ANN) Young (1967) proposed for the first time to use linear regression method to outline general operating rules from defined optimization After that, many authors in the world such as Yakowiz (1982), Teh (1985), Simonovic (1992), Wurbs (1993), Oliveira and Loucks (1997), Chen (2003), Kumphon (2013), Robin (2012 ), Mohsen Ahmadi et al (2015) applied the optimal technique for simulating reservoir system operation to build adaptive operating procedures for reservoirs However:  Although optimization and simulation are two different modeling approaches on characteristics, the clear distinction between these two directions is difficult because most models contain components of two above directions  It is necessary to have a simulation model in order to check the optimal procedure in the water reservoirs allocation process  Therefore, the simulation-optimization combination method has been formed to solve the problem of operating and distributing water sources of reservoir systems 1.1.3 Literarute review of reservoir water allocation using simulation-optimization method Carson and Maria (1997) presented a simple diagram of the optimal simulation model in reservoir water allocation (Figure 1.1) Under Legend: The blue column chart is the randomly generated data and the green part is the actual flow distribution Figure 2.2 The comparison of the actual flow probability distribution pattern and the random flow is generated by Monte Carlo simulation Thus, the generated random number sequence can be used in the optimization problem of reservoir operation, distribution of reservoir water appropriately in the river basin VGTB 2.3 Develop a model of operating multi-purposes reservoir system Steps to develop the optimization - simulation model in the thesis include: 1) Establish optimal issues in reservoir system operation; 2) Develop simulation model in reservoirs operation; 3) Develop an optimization model of search and connect with the simulation model of operating A Vuong, Song Bung 4, DakMi and Song Tranh reservoirs; 2.3.1 Study establishment Downstream control points Two hydrological stations of Ai Nghia and Giao Thuy were selected as two control points for water level / flow in the study The thesis uses the results of calculation of downstream water demand of the Ministry of Natural Resources and Environment in the Rule of inter-reservoir operation in the VGTB river basin No 1537 / QD-TTg dated 07/9/2015 Accordingly, ensuring the demand for downstream water uses is shown through the assurance of water level in Ai Nghia (Ai Nghia ≥ 2.67m) and in Giao Thuy (Giao Thuy ≥ 1.02m) Objective and objective function The objective of the study: To reasonable allocate water sources of VGTB river basins for various water-uses in order to maximize the electricity generation from hydropower plants, as well as ensuring the demand for water supply for economic sectors, livelihood and services in the dry season in VGTB river basin Objective function: The objective function of operating 04 reservoirs is displayed as:  n 25  F  M ax  9,81 * i , j * Qi , j ,t * H i , j ,t * t   n i 1 j 1 t 1  Where: F : Objective function to maximize electricity generated from A Vuong and Song Bung 4, Dak Mi and Song Tranh hydropower plants Qi,j,t : Average discharge of plant i, year j, at period t Hi,j,t: Average water column of plant i, in year j, at period t i,j: Total efficiency of turbine and generator of plant i in year j ∆t: Time step = 10 days; dry season includes 25 periods (from 16/12 previous years to 31/8 continuous year) n: number of years to simulated (10,000 years) i: number of hydropower plants, only 04 plants are focused as A Vuong, Song Bung 4, Song Tranh and Dak Mi Ei,t: electrical power of plant i at the period of "t" (kwh) Constraints on reservoirs and hydropower plants as: Constraints on water balance at reservoir node; Constraints on water balance at the flow node; Constraints on the smallest and largest storage volumes of reservoirs; Constraints on actual discharge for generation; Constraints on power generation capacity; Constraints on the relationship of bed reservoir topography; Constraints on discharge ~ downstream water levels; Constraints on demand of water supply at downstream: Ensuring water level at control points: HAi Nghia ≥ 2.67m; HGiao Thuy ≥ 1.02m 2.3.2 Develop optimization searching model and connect to reservoir operation simulation model The study uses OptQuest optimal module under the Crystal Ball model to develop the optimisation model then connected to the random inflow simulation model and reservoir operation simulation model to form the optimal operation model of A Vuong, Song Tranh 2, Song Bung 4, Dakmil reservoirs The objective function in the study is to optimize the power generation in dry season of 04 hydropower plants of A Vuong, Song Bung and DakMil and Song Tranh The thesis has searched for the optimal options (based on thousands scenarios to simulate electricity generation from hydropower plants, comply with defined constraints) to determine the most optional plan of power generation in dry season (December 16 to August 31 of the following year) in the system The opimisation search is applied as follows: - The inflow to each reservoir is randomly generated by Monte Carlo method and complies with the predefined hydrological correlation; Flow through turbines is used as a decision variable; The objective function is to maximize the total output of electricity, calculated according to the equation in Section 2.3.1 - Optquest module will conduct searching in multiple simulations to determine the maximum value of the objective function Figure 2.3 Simulation - optimization operation reservoir model of VGTB river basin Figure 2.4 optimization searching in the study 2.4 Develop a simulation model of inter-reservoirs operation with HEC-RESSIM Although the simulation-optimization reservoir operation model of Vu Gia - Thu Bon has been developted with many advantages in combining optimization and simulation techniques but there are still certain limitations includig: (1) it cannot confirm that the result is optimal or not because the model runs thousands of random options and selects the best option; (2) The simulation time step is 10 days, which makes it difficult to follow the Rule of inter-reservoir operation or actual operation Therefore, the PhD student select the model HEC-RESSIM to re-simulate the river reservoir system in the short time (1 hour) The purpose of the calculation is to re-examine the selected option, the objective function of the problem as well as the controlled water levels points in the downstream The HEC-RESSIM model has been set up with the following parameters: Up Border: - Vu Gia River: release discharge from reservoirs A Vuong, Song Bung 4, Dak Mi - Thu Bon river: release discharge to reservoirs Song Tranh and Dak Mi reservoirs Border for joint branches: the flow of middle areas of Bung, A Vuong, Cai, and Thu Bon rivers is taken according to the ratio of areas Calibration and verification of models: The data used to calibrate and verify the model are measured data of Nong Son, Thanh My (flow) hydrological stations in 2015 and 2016 Table 2.2 Result of Calibration and verification of models Location Thanh My Nong Son Calibration 0,9305 0,7514 verification 0,9762 0,8246 2.5 Conclusion of chapter The thesis has conducted research steps to establish a scientific basis for the coordination of water resource allocation for the system of 04 reservoirs, including: (1) Develop a random simulation model of the flow to reservoir which is considered the hydrological correlation in the system (2) Establish optimal study for operating reservoirs of A Vuong, Song Bung 4, Dak Mi and Song Tranh (3) Develop simulation model for operating 04 reservoirs (4) Optimal calculation and development of the optimization searching model in connection with the reservoir operation simulation model to determine the optimal operation process for power generation of A Vuong and Song Bung reservoir systems Dak Mi and Song Tranh (5) Develop the HEC-RESSIM model to simulate inter-reservoir operation systems of A Vuong, Song Bung 4, Dak Mi and Song Tranh The model has been calibrated and verified 1CHAPTER 3: CALCULATION RESULTS OF SYSTEM OPERATION IN VU GIA THU BON RIVER BASIN – TO IMPROVE EFFICIENCY OF WATER ALLOCATION 3.1 Identify scenarios to operate 04 reservoirs The study on operation of reservoirs system A Vuong, Song Bung 4, Dak Mi 4, Song Tranh is using the simulation - optimal operation model which will be having 10 scenarios, divided into 03 group as follows: Group 01: Calculated scenario under Rule No 1537 Base scenario: The release discharge rates of A Vuong, Song Bung and Dak Mi reservoirs comply with the provisions in Rule No 1537 Group 02: defined according to reservoir characteristics Scenario 1: Release discharge rates of A Vuong, Song Bung and Dak Mi reservoirs are equal to the ratioes of catchment area in the system Scenario 2: Release discharge rate of A Vuong reservoir is equal to release discharge rate of Song Bung reservoir (50% -50%) Scenario 3: The release discharge rates of reservoirs A Vuong, Song Bung and Dak Mi are equal to the ratio of yearly inflows to reservoirs Scenario 4: The discharge rates of reservoirs A Vuong, Song Bung and Dak Mi are equal to the ratio of inflows to reservoirs in dry season Scenario 5: The release discharge rates of reservoirs A Vuong, Song Bung and Dak Mi are equal to the proportion of the volume of corresponding reservoirs Group 03: Group of scenario defined according to reservoir characteristics with discharge rate of Dak Mi reservoir defined according to Rule No 1537 Scenario 6: The release discharge rate of reservoirs A Vuong and Song Bung are equal to the ratioes of catchment area in the system, one of reservoir Dak Mi is taken according to the Rule No 1537 Scenario 7: The release discharge rate of reservoir A Vuong and Song Bung are equal to the ratio of yearly inflows to reservoirs, the release discharge rate of reservoir Dak Mi is taken according to the Rule No 1537 Scenario 8: The release discharge rate of reservoir A Vuong and Song Bung are equal to the ratio of inflows to reservoirs in dry season, the release discharge rate of reservoir Dak Mi is taken according to the Rule No 1537 10 Scenario 9: The release discharge rate of A Vuong and Song Bung reservoirs are equal to the proportion of the volume of corresponding reservoirs, the release discharge rate of reservoir Dak Mi is taken according to the Rule No 1537 Each scenario is calculated with: + 25 random variables corresponding to each reservoir flow in each period in the dry season There are 100 random variables for four reservoirs in the system + 25 decision variables corresponding to discharge flow through each plant in each period in the dry season There are 100 decision variables + The main predictor variable is the total annual electrical output of 04 reservoirs in dry season + The constraint of water level at Giao Thuy is not less than 1.02m and at Ai Nghia is not less than 2.67m and constraints on reservoirs and hydropower + Each scenario is carried out through 5000 simulations with each simulation will conduct 2000 trials 3.2 Summary of calculation results of all scenarios Summary of calculation results using simulation - optimization model to operate 04 reservoirs with 10 scenarios can sum up with some conclusions: 1) All scenarios have total power output in dry season is greater than the actual one in 2015 and 2016 2) The highest power output is in scenario 5, reaching 1570.0 million kWh, higher 10.2 million kWh (0.6%) than base scenario; higher 88 million kwh (5.9%) and 170.1 million kwh (12.1%) compared to the actual electricity output of the reservoirs in 2015 and 2016 respectively, Compare among 04 reservoirs: 3) Power output in the dry season of A Vuong Reservoir is the largest, followed by Song Bung 4, Song Tranh and Dak Mi Figure 3.1 Power output in the dry season In terms of power output, scenario is selected as the optimal scenario Group of Scenario Group of scenario Figure 3.2 Optimal operation curve by all scenarios Sum up with the operation curve of reservoirs of A Vuong, Song Bung 4, Song Tranh and Dak Mi for 10 scenarios, some conclusions can be showed as follows: 1) Most operating curves of 04 reservoirs violate the regulated restriction water supply curves of each reservoir according to the Rule No 1537 2) The inter-reservoir operation curve under Scenario is less violation compared to others In terms of inter-reservoir operation curve, it is proposed to select scenario (The discharge rate of A Vuong, Song Bung and Dak Mi reservoirs is equal to the proportion of the corresponding reservoirs’ volumes) is the optimal scenario Therefore, PhD student proposed to select scenario for detailed calculation by HEC-RESSIM model, because this scenario is more optimal in production power and operating trajectory than the other scenarios 3.3 Using HEC-RESSIM model to details calculate selected scenarioes In order to evaluate the effectiveness of the optimal operation plan, the PhD student use the HEC-RESSIM model to calculate and analyze options for operating the reservoir system in dry season from December 16 prevous year to December 31 next year: 1) Option 1: Minimum release discharge from 04 reservoirs according to the Rule No 1537; 2) Option 2: Minimum release discharge from 04 reservoirs according to the selected Scenario 5; Each option is calculated with cases: 1) inflow data is according to the actual measured data in 2015, 2016 (after all reservoirs have entered electricity generation); and 2) inflow data is for the period 1981-2008 (before building 04 reservoirs on Vu Gia - Thu Bon river) 3.3.1 Simulation of operation in 2015 and 2016 Figure 3.3 illustrates the results of the operation simulation of 04 reservoirs with inflow data according to the actual measured data of 2015 and 2016 Figure 3.3 The results of operation simulation of 04 reservoirs with flow data according to the actual data of 2015 and 2016 Table 3.1 Summary of calculation results of electricity output by each reservoir power generated in dry power generated in dry seasons 2015 (MWh) seasons 2016 (MWh) Resevour Option Option Option Option A Vương 435.915 448.083 427.508 416.455 Bung River 260.518 257.371 192.646 164.063 Đăk Mi 158.301 212.726 162.982 210.654 Tranh River 305.211 322.985 229.839 231.639 Total 04 1.159.945 1.241.165 1.012.975 1.042.811 resevours Comment: Electricity output of alternative in the dry season of reservoirs A Vuong, Song Bung 4, Dak Mi and Song Tranh is greater than the option for both years 2015 and 2016 The corresponding difference for each year is 7.00% (2015), equivalent to 81,220 MWh and 2.94% (2016) equivalent to 29,836 MWh in the dry season Considering water level at downstream, the results of water level calculation at Ai Nghia and Giao Thuy show that the water level at Ai Nghia and Giao Thuy is higher than the control water level of 2.67m and 1.02m respectively 3.3.2 Simulation of operation in 1981-2008 This is the period before the operation of reservoirs in the system The author has calculated the annual regulation for each year, comparing the electricity output of each year in the period 19822008 and follow Options and Figure 3.4 Total power generated in dry seasons 1981-2008 Comment: Electricity production in the dry season of each year in the period 1982-2008 of reservoirs A Vuong, Song Bung 4, Dak Mi and Song Tranh according to option is greater than the power output of 04 reservoirs operated by Procees No.1537 (Option 1) The lowest difference was 1.12% (1996), equivalent to 20,067 MWh and 11.20% (1994), equivalent to 157,145 MWh in the dry season Therefore, it can be concluded once again that the interreservoirs operated under Scenario (with release discharge rates of reservoirs A Vuong, Song Bung and Dak Mi is equal to the proportion of the corresponding reservoirs’ volumes) has advantages regarding the electricity generation, compared to the Rule No 1537 and still ensures water demand at downstream 2CONCLUSIONS AND RECOMMENDATIONS The study has developed the random simulation model of inflow to the reservoirs considering the hydrological correlation in the system The model includes components such as: Analyzing to find out the probability distribution for each month's flow to each reservoir; Generate a random inflow to the above reservoirs using the Monte Carlo method which taken into account the uniformity of the flow regime based on the hydrological correlation among the river branches from the actua data This is an important baseline calculation providing input data for simulation and optimization models The optimization searching model with connection to reservoir operation simulation model to determine the optimal operation plan of the reservoirs system of A Vuong, Song Bung 4, Dak Mi and Song Picture is developed in the thesis Based on the combining model of simulation and optimization techniques, the inter-reservoir operation process is selected, analyzed, established and calculated according to 10 scenarios Results of the interreservoir operation are feasible when all 10 scenarios have a higher power productions than actual ones in 2015 and 2016 The calculation results show that the largest power output is in the scenario reached 1570.0 million kwh, 10.2 million kwh (0.6%) higher than the baseline scenario calculated under Rule No.1537; which is 88 million kwh (5.9%) higher and 170.1 million kwh (12.1%) higher than the actual operating of those reservoirs in 2015 and 2016 This is also an orbital scenario of inter-reservoir under water supply curve The optimal inter-reservoir operation Rule is identified in the thesis (the release discharge rate of reservoirs A Vuong, Song Bung and Dak Mi is equal to the proportion of reservoir’s volumes Scenario 5) The the selected operation process is tested by the HECRESSIM model The scientific research is completed when integrating reservoir operation simulation model of HEC-RESSIM for the optimal Rule from simulation-optimal model The results of operation calculation for the 27 years from 1982 to 2008 (the period before the reservoirs’ operation) and the period of years 2015-2016 (after all reservoirs have been operated) shows the power production of optimal Rule is greater than operated according to the inter-reservoir operation Rule of the Ministry of Natural Resources and Environment (Rule No 1537), the difference is from 1.12 % (1996) equivalent to 20,067 MWh to 11.2% (1994) equivalent to 157,145 MWh With the above results, the thesis identifies two new contributions, including:  Develop a scientific basis for operating the reservoir system in water allocation of VGTB river basin in dry season;  Initially, propose the optimal operation Rule of the four largest reservoirs in the VGTB river basin including (A Vuong, Song Bung 4, Dak Mi and Song Tranh reservoirs) to ensure maximum electricity production and harmonization with water demand at downstream; Recommendation The study of the thesis is quite detailed with many different operating scenarios applying simulation - optimizing operation of inter-reservoir system In order to reduce time in calculation, the evaluation of the downstream water level assurance is based only on hydrological models through consideration of the relationship between flow and water level at the control points To be able to assess more accurately, it is possible to use a hydraulic model to consider the effect of water level fluctuations due to the operation of discharging water from upstream reservoirs to the water level at the control points Applied to other river basins has similar conditions, in particular in ones in central Vietnam ... AND OPERATING THE SYSTEM OF RESERVOIRING FOR VU GIA THU BON RIVER BASIN - IN THE DRY SEASON 15 2.1 Introduction of reservoir system in Vu Gia - Thu Bon river basin and select reservoirs for... vực sông Vu Gia – Thu Bồn mùa cạn mơ hình HEC-RESSIM, Tạp chí Khoa học kỹ thu? ??t thủy lợi Môi trường 09/2018; Tô Việt Thắng (2018), Method for optimal water allocation of reservoirs system – a casestudy... RESOURCES AND OPERATING THE SYSTEM OF RESERVOIRS FOR VU GIA THU BON RIVER BASIN - IN THE DRY SEASON 2.1 Introduction of reservoir system in Vu Gia - Thu Bon river basin and select reservoirs for research